1. Field of the Invention
The present invention relates to a physical vapor deposition, and more particularly, to an RF (radio frequency) sputtering sputtering apparatus and a film formation method using the same, capable of appropriately improving quality of a film being deposited on a wafer.
2. Description of the Background Art
The forming method of a film on a wafer may vary to a chemical method in which a gaseous material is synthesized via a chemical reaction into a solid material in form of a film or particles, and a physical method in which target particles are deposited on a wafer using a variety of physical technologies.
The chemical method includes a chemical vapor deposition (CVD) and a plating, and the physical method includes a sputtering, evaporation and spin coating.
FIG. 1 is a schematic construction view illustrating a conventional sputtering apparatus. As shown therein, the sputtering apparatus includes a substrate 16 mounted thereon by a wafer W, a chamber 14 including a target 18 (cathode) serving as a deposition material and separated from an exterior thereof, a gas supply unit 24 providing gas into the chamber 14, a power supply unit 22 providing an RF power to respective sections, and a vacuum unit 30 vaccumizing the chamber 14.
The target 18 is formed of one selected from a ceramic material, metal compound and insulation material. Argon gas (ArO.sub.2) is used for the gas.
The RF power supplied from the RF power supply unit 22 is provided to the target 18 via the cable 26 and a matching network 28.
Reference numeral 32 denotes an ion sheath, and 34 denotes a base plate, respectively.
According to the conventional film forming method using the apparatus in FIG. 1, gas is supplied between the target 18 and the substrate 16 under a vacuum state. When the RF power is applied to the target 18, the gas becomes ionized by a glow discharge so that a plasma discharge occurs between the target 18 and the substrate 16. The positive-charged ions which exist in the discharge region become striking the surface of the target 18 by an electrical power, whereas atoms or molecules sputtered from the target 18 become deposited on the wafer W facing thereagainst.
FIGS. 2A and 2B are graphs illustrating the substrate, the target and plasma potentials during a film forming process using the apparatus in FIG. 1. With reference to the drawings, their inter-electrical relation and bombarding phenomenon will now be described.
As shown in FIG. 2A, when using argon+oxygen gas (Ar+O.sub.2) as a process gas, the positive-charged ions (Ar.sup.+) within the plasma continues its acceleration toward the target in accordance with an electrical force caused by a potential difference (Vp&gt;Vt) of a target potential Vt and a plasma potential V.sub.p, thereby striking the target surface. The atoms sputtered from the target by the strike of the positive-charged ions are deposited on the wafer. However, some of the positive ions within the plasma become accelerated toward the substrate during the deposition by an electrical force caused by a potential difference (Vp&gt;Vs) of the plasma potential Vp and the substrate potential Vs, thereby eventually bombarding the film on the wafer.
Referring to FIG. 2B, when argon gas is used as a process gas, a negative dc self-bias voltage Vdc is induced to the target, so that a plasma potential is decreased, thereby decreasing the bombarding of the positive ions within the plasma onto the substrate surface. In the meantime, the negative ions (O.sup.-) sputtered from the target become accelerated by the voltage Vdc induced to the target, thereby bombarding the film deposited on the wafer.
The conventional film formation method as described above has a disadvantage in that the film deposited by a sputtering method becomes bombarded by both the positive ions within the plasma and the negative ions sputtered from the target for thereby incurring a resputtering phenomenon in the film itself.
Further, when the film is formed on the substrate using a ceramic material as a target, the composition of the ceramic film deposited on the substrate becomes different from that of the source target due to the different sputtering yield among the respective components incorporating the ceramic material, thereby making it difficult to control the composition of the film being deposited on the substrate.
Still further, an electrical crystalline film characteristic of the film deposited on the substrate may be significantly deteriorated by the bombarding which results from both the positive ions within the plasma and the negative ions sputtered from the target.